Mimir's Head

During your upkeep, you may take the top
card of your library and exchange it with a opponent for a card in their hand. Cards exchanged this way lose their mana cost and
now only cost {4} to cast for both cards. (Opponents do not have to reveal their hands
and you do not have to reveal the top card of
your library)
Aesir, Vanir, Giants... I broke peace with all.